The present invention relates to contact pins adapted to be inserted into metal-coated bores of circuit boards which contact pins include guide sections and successive contact and connecting sections.
Electrical connections with certain points of circuit boards or contact panels are often established by the insertion of contact pins directly into metal-coated bores in the contact panels. For various reasons, mainly however because the electrical connections are usually established by automatic manufacturing equipment, the contact pins have guide sections at their front ends, which guide sections are somewhat smaller in cross-section than the metal-coated bores of the contact panels so that insertion of the pins into the bores is facilitated and the contact pins are automatically centered during insertion into the bores. Axially adjacent the guide section there is provided the contact section which is that part of a contact pin which provides for good electrical contact with the metal layer on the inner walls of the bores. The metal layer or coating is relatively thin; it has generally a thickness of several .mu., up to 1/100 mm in exceptional cases. As a result of manufacturing methods however the tolerances for the bore diameter are relatively large; they may be in the area of 2/10 mm.
In spite of such large tolerances in bore diameters the contact surfaces of the contact pins should be in contact with the metallic inner surfaces of the bores with a predetermined minimum contact pressure and this minimum pressure should be maintained as long as the pins are disposed in the bores.
It is further desirable that, upon insertion of the pins into the bores, any contact surface oxidation layer or any other surface deposits including gas molecules are removed so that, after insertion of the contact pins, there is full metallic contact established between the contact surfaces of the pins and the inner metallic surfaces of the bores. In spite of these requirements the thin metallic contact layers on the inner surfaces of the bores must not be damaged. Damage to those contact layers would not only cause admission of gases resulting in a slow oxidation of the contact surfaces but might even, upon removal of a contact pin and insertion of a new pin, adversely affect the possibility for the new pin to make good contact.
Prior art contact pins are generally provided with axial slots so that the remaining outwardly bent web structures can be resiliently compressed in order to achieve the resilient engagement of the pin contact surfaces with the metal-coated bore walls.
These kinds of contact pins generally engage the contact surfaces of the bores in the desired manner once they are disposed in the bores but they usually damage the metal layers on the inner surfaces of the bores since, although the resiliency of the web structures is adequate in the axial centers of the webs, there is insufficient resiliency at the end portions of the webs. These relatively rigid ends of the webs damage the thin metal layers of the bores upon insertion of the pins if the contact pins are only slightly oversized or the bores are slightly undersized.
The same undesirable results are achieved with other known contact pins such as V-shaped or W-shaped pins.
All these contact pins have the disadvantage that they are not sufficiently resilient in the interface areas between the guide sections and the contact sections such that the metal coatings of the bores are generally damaged if the pins are slightly oversized or the holes are slightly undersized. If, on the other hand, the pins are slightly undersized or the holes are slightly oversized, the contact pin engagement with the contact surfaces of the bores is usually insufficient.
The reason for the rigidity of the webs at the interface area of guide and contact sections is that these areas are the origins of the web structures such that the lever length of the springs is very small or practically zero and, as a result, the resiliency of the web structures is zero at this point where the contact structures first come into contact with the thin metal layers of the contact bores.
It is the principal object of the present invention to provide a contact pin which fulfills all the requirements pointed out earlier and which will not damage the contact metal layers of the bores into which the pin is inserted whether or not the pins or bores are under or over size as long as they are within certain tolerance limits.